The invention relates to a system and a method for monitoring an exhaust gas sensor in an engine downstream of an exhaust catalyst.
To meet current emission regulations, automotive vehicles must regulate the air/fuel ratio supplied to the vehicles"" engine cylinders to achieve maximum efficiency of exhaust gas catalysts. For this purpose, it is known to control the air/fuel ratio of internal combustion engines using an exhaust gas oxygen sensor positioned in the exhaust stream from the engine. The exhaust gas sensor provides feedback data to an electronic controller that calculates desired air/fuel ratio values over time to achieve optimum efficiency of a catalyst in the exhaust system. It is also known to have a system with two exhaust gas sensors in the exhaust stream in an effort to achieve more precise air/fuel ratio control with respect to a catalyst operational window. Normally, a pre-catalyst exhaust gas oxygen sensor is positioned upstream of the catalyst and a post-catalyst exhaust gas oxygen sensor is positioned downstream of the catalyst.
In connection with an engine having two groups of cylinders, it is known to have two exhaust manifolds coupled thereto where each exhaust manifold has a catalyst as well as pre-catalyst and post-catalyst exhaust gas sensors. Each of the exhaust manifolds corresponds to a group of cylinders in the engine. The feedback signal received form the exhaust gas sensors are used to calculate the desired air/fuel values in their respective group of cylinders at any given time.
Known engine control systems have also implemented strategies for determining when a pre-catalyst exhaust gas sensor becomes degraded. However, known engine control systems assume that post-catalyst exhaust gas sensors do not degrade since the sensors are buffered from a majority of the exhaust gases by an upstream catalyst. Thus, when a post-catalyst exhaust gas sensor does degrade, an engine control system using a degraded output signal from the post-catalyst exhaust gas sensor will be unable to maintain optimal air/fuel mixtures for optimal catalyst efficiency. Thus, the degraded sensor may result in increased emissions and decreased fuel economy.
The inventors herein have recognized that there is a need for a system and method that determines when a post-catalyst sensor becomes degraded.
The foregoing problems and disadvantages are overcome by a system and a method for monitoring a post-catalyst exhaust gas sensor in an engine in accordance with the present invention. The engine includes a first cylinder bank coupled to a first catalyst and a first exhaust gas sensor disposed downstream of the first catalyst. The first exhaust gas sensor generates a first signal. The method for monitoring the exhaust gas sensor includes supplying a first air-fuel mixture that is on average rich of stoichiometry to the first cylinder bank to remove oxygen stored in the first catalyst. The method further includes supplying a second air-fuel mixture that is on average lean of stoichiometry to said first cylinder bank to supply oxygen to the first catalyst. Finally, the method includes indicating that the first exhaust gas sensor is degraded when the first signal does not indicate a lean air-fuel ratio after supplying the second air-fuel mixture for a first predetermined time period.
A system for monitoring an exhaust gas sensor utilized in an engine is also provided. As discussed above, the engine includes a first cylinder bank coupled to a first catalyst. The system includes a first exhaust gas sensor disposed downstream of the first catalyst generating a first signal. The system further includes a controller operably coupled to the first exhaust gas sensor. The controller is configured to supply a first air-fuel mixture that is on average rich of stoichiometry to the first cylinder bank until the first signal indicates a rich air-fuel ratio. The controller is further configured to supply a second air-fuel mixture that is on average lean of stoichiometry to the first cylinder bank to supply oxygen to the first catalyst. Finally, the controller is configured to indicate the first exhaust gas sensor is degraded when the first signal does not indicate a lean air-fuel ratio after supplying the second air-fuel mixture for a first predetermined time period.
Thus, the inventive system and method can determine when a post-catalyst exhaust gas sensor becomes degraded.